297 research outputs found
Local moment, itinerancy and deviation from Fermi liquid behavior in NaCoO for
Here we report the observation of Fermi surface (FS) pockets via the
Shubnikov de Haas effect in NaCoO for and 0.84,
respectively. Our observations indicate that the FS expected for each compound
intersects their corresponding Brillouin zones, as defined by the previously
reported superlattice structures, leading to small reconstructed FS pockets,
but only if a precise number of holes per unit cell is \emph{localized}. For
the coexistence of itinerant carriers and localized spins on a paramagnetic triangular superlattice leads at low temperatures
to the observation of a deviation from standard Fermi-liquid behavior in the
electrical transport and heat capacity properties, suggesting the formation of
some kind of quantum spin-liquid ground state.Comment: 4 pages, 4 figure
Severe Fermi Surface Reconstruction at a Metamagnetic-Transition in CaSrRuO (for )
We report an electrical transport study in CaSrRuO single
crystals at high magnetic fields (). For , the Hall constant
decreases sharply at an anisotropic metamagnetic (MM) transition
reaching its value for SrRuO at high fields. A sharp decrease in the
coefficient of the resistivity -term and a change in the structure of
the angular magnetoresistance oscillations (AMRO) for rotating in the
planes, confirms the reconstruction of the Fermi surface (FS). Our observations
and LDA calculations indicate a strong dependence of the FS on the Ca
concentration and suggest the coexistence of itinerant and localized electronic
states in single layered ruthenates.Comment: 5 pages, 4 fig
Multi-band superconductivity in LaFeAsO_{0.9}F_{0.1} single crystals probed by high-field vortex torque magnetometry
To probe manifestations of multiband superconductivity in oxypnictides, we
measured the angular dependence of the magnetic torque in the
mixed state of LaOFFeAs single crystals as a function of
temperature and magnetic fields up to 18 T. The paramagnetic
contribution of the Fe ions is properly treated in order to extract the
effective mass anisotropy parameter from
. We show that depends strongly on both and ,
reaching a maximum value of 10 followed by a decrease towards values
close to 1 as is lowered. The observed field dependencies of the London
penetration depth and suggest the onset of suppression
of a superconducing gap at .Comment: 7 pages, 7 figure
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